The invention relates to cigarette making machines or the like. More specifically, the invention relates to an apparatus for forming a tobacco stream for the production of rod-shaped smokers' articles in cigarette making machines or the like comprising a tobacco channel defind by an air-permeable bottom and fixed sidewalls and having a stream building section which is adjacent to a tobacco building duct and a discharge end a tobacco band which travels in the longitudinal direction above the channel bottom, a trimming device for removal of surplus from the tobacco stream, and with means for applying different suction to successive sections of the tobacco channel.
Within the meaning of the present invention, rod-shaped smokers' articles are understood to embrace smokable articles, such as cigarettes, cigarillos, cigars and the like, which are produced from tobacco or tobacco substitute materials in accordance with the rod forming technique.
In conventional cigarette making machines, the distributor discharges into a substantially vertical tobacco supplying duct which guides a tobacco shower upwardly in an upwardly directed air stream. The upper closure of the duct is constituted by a section of a tobacco channel which extends substantially horizontally and transversely of the tobacco supplying duct and has an air-permeable bottom along which is guided a travelling air-permeable tobacco band whereon the particles of tobacco, which are delivered in the form of the tobacco shower, are built up to form a cigarette filler stream. This section of the tobacco channel, which extends into the tobacco feeding duct, will hereinafter be referred to as the stream building section. During transport through the tobacco channel, the tobacco stream which is showered onto the tobacco band is held on the latter by suction which is applied to the bottom of the channel from the rear side of the channel.
The tobacco band transports the tobacco stream in the tobacco channel out of the stream building section to a trimming device which removes surplus from the stream. Downstream of the trimming device, the stream is transported to a depositing station and is deposited onto a wrapping strip, e.g., a strip of cigarette paper.
It is known to apply different suction to successive sections of tobacco channel by resorting to divided suction chambers. For example, DE-OS 19 62 476 discloses an apparatus wherein a portion of a suction chamber is adjacent to the tobacco channel in the tobacco supplying duct and a second part of the suction chamber is adjacent to a section of the tobacco channel which follows downstream. Suction in that part of the suction chamber which is adjacent to the downstream section of the tobacco channel is variable in order to allow for regulation of the removal of surplus by more or less pronounced loosening of the stream during transport to the trimming device.
DE-PS 11 57 124 dicloses an apparatus wherein the bottom and the sidewalls of a tobacco channel are formed by travelling bands. Upstream of the trimming device, there is provided a series of successive suction chambers which apply suction to the bottom of the tobacco channel in such a way that suction decreases in the direction of transport. No suction is applied to the tobacco stream in the region of the trimming device proper. The reduction of suction upstream of the trimming device should effect a gradual loosening of the tobacco stream. In the apparatus according to DE-OS 30 41 694, suction in the tobacco channel outside of the stream building section is increased by a separate part of the suction chamber in order to prevent a loosening of the stream or a separation of particles from the band.
When the stream is moving at elevated speeds, such as are required in modern high-output machines, eddy currents which develop at the locus of entry of the tobacco stream into the tobacco channel and at the upper side of the stream cause the development of turbulences in the upper layers of the tobacco stream. This brings about changes in the buildup of the stream ahead of and behind the trimming device, not only transversely of the stream but also in the longitudinal direction of the stream which, of course, can adversely influence the quality of the produced smokers' articles. A longitudinal shifting of stream sections of greater density which are developed within the stream simultaneously with removal of the surplus by the trimming device for the purpose of head reinforcement, can constitute a particularly negative influence.